Light Detection and Ranging (LIDAR), is a remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances) to an object. In particular, light is transmitted towards the object and the time it takes to return to its source is measured. This is also referred to as measuring time-of-flight (TOF).
LIDAR sensors are an essential element in future fully autonomous or semi-autonomous self-driving cars. The system operates on the principle of TOF measurement. A very short laser pulse is transmitted, hits an object, is reflected and detected by a sensor. From the time-of-flight of the laser beam it is possible to calculate the distance to the object. Scanning LIDAR systems scan the surroundings of the car horizontally with a laser beam across a certain angular segment and produce a three-dimensional (3D) map of the environment. In most cases, the laser beams in present-day scanning LIDAR systems are deflected by means of mechanical moving mirrors (i.e., microelectromechanical systems (MEMS) micro-mirrors). Some solutions make use of several laser diodes mounted one on top of the other to extend the vertical field of view.
In current LIDAR systems, a chip assembly may be used with a tilted protective glass arranged over a MEMS micro-mirror. The glass is tilted in order to reduce the amount of light reflected off the back side of the glass back onto the MEMS micro-mirror, referred to as static reflection. The static reflection back onto the MEMS micro-mirror would cause inaccuracies, including a “blurring” in the return image. However, this method has a disadvantage in that it results in a non-planar package outline that complicates a full automatic board assembly process.